This application relates to and incorporates herein by reference Japanese Patent Applications No. 11-185672, No. 11-185673, No. 11-185674 and 2000-46421 filed Jun. 30, 1999, Jun. 30, 1999, Jun. 30, 1999 and Feb. 23, 2000, respectively.
The present invention relates to an electrical load control apparatus which makes an operation response characteristic thereof faster by discharging electrical energy accumulated typically in a capacitor. The present invention may be applied to an electromagnetic valve for injecting fuel to improve opening response of the electromagnetic valve.
It is proposed to speed up the opening response of an electromagnetic valve that energy accumulated in a capacitor by using a voltage raising circuit such as a DC-DC converter is discharged to drive the electromagnetic valve. Energy is accumulated in the capacitor to be to passed through the electromagnetic valve. This conventional technique is disclosed in U.S. Pat. No. 5,907,466 (JP-A-9-115727), U.S. Pat. No. 4,604,675 (JP-B2-7-78374) and U.S. Pat. No. 5,532, 526 (JP Patent 2598595).
In addition, in recent years, it is proposed to attain another injection with a timing different from the timings of the conventional injections as a solution to reduce exhausted emissions. Such an another injection is injections (multi-stage injections) other than normal pilot and main injections, that is, multiple injections before and after the pilot and main injections which are carried out under injection control in a diesel engine. Alternatively, such an another injection is an injection carried out in the course of an injection of another cylinder in a multi-cylinder injection system.
In multi-stage injections or multi-cylinder injections involving a plurality of cylinders, injections with different injection periods are carried out at different intervals during a short period of time such as the period of a combustion process and, in addition, the number of cylinders involved in the injections also varies as well. In order to meet such requirements, in an apparatus disclosed in JP-A-10-205380, a capacitor is used for accumulating energy with an amount large enough for accomplishing a plurality of injections in advance. During a period of time between the start of an injection and an event in which the voltage of the capacitor drops to a level below a predetermined electric potential, energy is supplied from the capacitor to the electromagnetic valve.
However, this apparatus is incapable of ensuring that energy of a desired amount be accumulated in the capacitor. That is, the quantity of energy accumulated in the capacitor prior to the start of an injection including energy recovered from the electromagnetic valve varies from injection to injection so that a voltage appearing at the capacitor before an injection also varies from injection to injection. Thus, in the conventional technique of supplying energy from the capacitor to the electromagnetic valve during a period of time between the start of an injection and an event in which the voltage of the capacitor drops to a level below a predetermined electric potential, the quantity of the energy and the speed to supply the energy from the capacitor to the electromagnetic valve vary in accordance with the voltage of the capacitor appearing at the start of an injection. As a result, the conventional apparatus fails to assure a uniform degree of opening of the electromagnetic valve and a uniform response characteristic thereof. Thus, the electromagnetic valve is not driven to operate in a stable manner.
It is thus an object of the present invention to ensure a stable operation of an electrical load driven by an apparatus by using energy accumulated in energy accumulation device such as a capacitor.
According to one aspect of the present invention, an electrical load is driven with a current which varies with an accumulated energy level. That is, the electrical load is provided with electric energy for speeding up an operating response of the electrical load during an operation period of the electrical load at a timing dependent on an energy accumulation level in an energy accumulation device. In the case of a capacitor, the energy accumulation level is the voltage of the capacitor. Thus, energy is supplied at a timing independent of whether the energy accumulation level is high or low, assuring a desired operation.
In addition, the electrical load is preferably provided with energy for speeding up an operating response of the electrical load in accordance with the voltage of a vehicle-mounted power supply with a delay timing and in such a manner that, the lower the voltage of the vehicle-mounted power supply, the more the timing to start the operation of the electrical load is expedited.
According to another aspect of the present invention, the energy supply from an energy accumulation device such as a capacitor is stopped based on a current flowing through the electrical load.
According to a further aspect of the present invention, an energy accumulation device such as a capacitor is set to retain an offset of at least a predetermined quantity to be left in the energy accumulation device when energy of a counter-electromotive force is recovered at the end of a period to supply energy to an electrical load. With an offset of a predetermined quantity left as a capacitor voltage, it is thus possible to electrically charge and discharge the capacitor in the area where the valve closing time slightly varies with a change in capacitor voltage so as to make the valve closing time remain virtually unchanged.
According to a still further aspect of the present invention, electrical loads not driven at the same time among a plurality of electrical loads are put in a group, and energy from an energy accumulation device is supplied to the group of electrical loads. Thus, the number of energy supplying devices can be reduced.